A cute little upright bird in a dinner suit waddling along an ice floe. That’s the usual image brought to mind by the word “penguin”—an image epitomised by the Adelie penguins of Antarctica, and used in advertising the world over.
However, most of the world’s 18 penguin species do not fit the Adelie mould. Rockhoppers, one of the most numerous penguins, are a case in point. These gregarious birds certainly have “dinner suits,” but they hop as much as waddle, and most never even get to see ice floes, let alone walk on them. Cute? To some eyes, perhaps, but behind their long yellow eyebrow tassels and bright red eyes lies an aggressive nature that has landed them a reputation as the punks of the penguin world.
Unlike Adelie and emperor penguins, rockhoppers are not true Antarctic penguins but are birds of the subantarctic, frequenting the waters around or just north of the Antarctic convergence. The convergence marks the meeting of the cold Antarctic and relatively warm subantarctic waters. It meanders around the globe mostly between the 50th and 60th parallels. To the south, upwellings of nutrient-rich water support a density of marine life that is unmatched in any other ocean. Rockhoppers, along with other seabirds and whales, take advantage of the banquet, much of which is in the form of small shrimp-like krill.
In the subantarctic latitudes, it is the ocean which dominates, covering 98 per cent of the earth’s surface.
Only the toe of South America and a few scattered islands stand in the path of the prevailing westerlies which blow unimpeded clean around the globe.
For the huge number of seabirds in the region, these specks of land are the only nesting places within striking distance of the rich southern feeding grounds. New Zealand’s subantarctic islands (Bounty, Antipodes, Snares, Auckland and Campbell), strung out to the south and southeast of the South Island, are no exception. Hundreds of thousands of petrels, albatrosses and penguins gather on these islands each summer.
Rockhoppers congregate on the southernmost, Campbell Island, which lies six hundred kilometres south of Stewart Island. Some 100,000 birds come ashore each year in 15 separate colonies, most of which are on the exposed west and southwest coasts. Hemmed in by high cliffs, the birds nest among boulders on the steep slopes that run down from the cliffs to the sea. Not for them the quiet bays or sheltered harbours which other penguins choose as breeding sites.
Rockhoppers are not confined to Campbell Island. They breed on a large number of islands throughout the Southern Ocean. From their northern limit on temperate Tristan da Cunha in the South Atlantic to Australia’s icy Heard Island in the southern Indian Ocean, they encircle the earth. Their present stronghold is the Falkland Islands, where perhaps three quarters of the world’s 10 million rockhoppers breed.
Rockhoppers belong to the genus Eudyptes, Greek for good diver. “Feathered fish,” sailor Admiral Beaulieu called them after seeing them for the first time. It’s not far from the truth. Penguins are as much at home in the sea as is a dolphin or whale. They fly through the water, flapping their small wing-like flippers and using their feet as rudders.
Penguins have close to neutral buoyancy in water, so little energy is required for either diving under the sea or floating on top. Like all divers—humans included—penguins run the risk of developing high nitrogen concentrations in the blood during deep dives, a situation that can lead to decompression sickness (“the bends”). Some animals, such as seals, avoid this problem by exhaling 50-60 per cent of the air in their lungs before diving. Surprisingly, penguins appear to dive after breathing in. Rockhoppers probably don’t dive deep enough (less than 70 metres) or long enough (under two minutes) for the bends to be a problem, but some penguins do, seemingly defying the laws of chemistry.
If penguins are so at home in the sea, why the need to come ashore?
Firstly, to breed. Eggs can’t be laid, nor chicks reared, in the ocean—there is no method of keeping them warm enough. On land there are also fewer dangers for penguins and their offspring.
Secondly, to moult. Like all birds, penguins have a covering of feathers, although their plumage differs from that of aerial birds in that it is very uniform, lacking large flying feathers. The main function of penguins’ scale-like covering is to insulate, as these birds live in environments that are much colder than their body temperature.
When the feathers are lying flat they form a nearly water- and airtight surface. Underneath the top waterproofing feathers are small, dry downlike feathers that trap air to form an effective insulating layer. Beneath that again is a layer of blubber.
In warm weather, penguins puff up their plumage to allow air to circulate, and open small capillaries near the skin’s surface (especially on the feet) to allow blood to cool. Rockhopper chicks often stand in their parents’ shadow to keep cool, or flop down on to the nest, flippers and feet spread out, panting.
Feathers wear out, so once a year penguins need to moult. During this 3-5-week period they cannot enter the water—and therefore cannot feed—because without adequate insulation they would die of hypothermia.
A penguin’s need to periodically leave the sea has made the birds vulnerable to humans. Slow and clumsy on land, and conveniently grouped together in large colonies, they made easy pickings for hunters who slaughtered them for their skins, feathers and fat.
One of the most notable cases of penguin exploitation took place on Macquarie Island, in Australian territory. For over 20 years, royal penguins, relatives of rockhoppers, were killed and boiled down for their oil—up to 150,000 birds annually. At the peak of the season 2700 birds a day were rendered down. Remarkably (as claimed at the time by the licencee, Joseph Hatch, and supported by subsequent study), the killing made little impact on the island’s 2.5 million-strong royal penguin population, and the species flourishes there today.
Rockhoppers have had their fair share of exploitation, too—perhaps more than most species. Inhabitants of Tristan Da Cunha killed them for their tassels, skin and feathers. On Campbell Island, turn of the century whalers blew rockhopper eggs to be sold as curios in New Zealand. Falkland Islanders still collect rockhopper eggs, although today the activity is on a sustainable basis, eggs being taken at a time when the birds will lay again.
Punctually on october 7 every year, the first rockhopper penguins fight their way ashore on the rocky west coast of Campbell Island. They head for the same rookeries that they grew up in, and usually for the same nest site as last year to meet with their mate. These first birds are males, which are heavier than females and have slightly thicker bills. On arrival, they promptly set about claiming territory, then start building nests in preparation for the their mates’ arrival several days later.
At that point, some male penguins will find they haven’t got a mate, either through death or “divorce.” They will then set out to attract a new one, using a trumpeting display to get attention. Bowing towards the ground, they let out some short grunts, then, holding their flippers back and arching their heads towards the sky with open beaks—chests throbbing, tassels shaking—they give out a series of loud stuttering cries.
Finding a new mate is not something they can take their time about, as eggs must be laid and hatched, and chicks fledged before the end of the short southern summer.
Nests are not elaborate, just a small scraping on any relatively flat piece of earth or rock. Pebbles, bones or pieces of vegetation are gathered (or stolen from other nests) to build a simple bowl. The male collects the material and the female forms the scrape by lying on her belly and raking with her feet.
This small patch of ground becomes home for the next few months, and the owners will defend it from all corners. Loud squawks and sharp pecks will greet anything venturing on to each pair’s piece of real estate. Early explorers write of visiting rockhopper colonies and having the penguins latch on to clothing and refuse to let go, even if lifted clean off the ground.
Rockhopper sounds are not exactly in songbird class. Nevertheless, the screeches, squeals, grunts, sneezes—even the odd honk—are as important to penguin society as speech is to ours. Each sound is associated with a physical display, used for such things as establishing pair bonds, advertising availability, showing appeasement or status, or even just to let other penguins know you are around.
With an average of two nest sites to the square metre, rockhopper colonies are like overcrowded cities, with neighbours staying just out of pecking range. There is safety in numbers, though. Fighting off a determined skua—large hawklike “gulls” which scavenge around penguin colonies—is more than a bird can handle alone. A colony provides some measure of protection, especially for eggs and chicks.
Within these crowded rookeries, arguments rage. The theft of nesting material, or even a small incursion into a neighbour’s territory, calls for an attack. Seizing each other with their beaks, the penguins twist and turn until one bird gains the upper hand by getting hold of the nape of the other’s neck. It then begins beating its adversary furiously with its flippers. Add to this duel the squawking and encouragement of neighbours and it becomes a scene of general mayhem.
Such scraps usually last for less than a minute. Occasionally, though, more serious fights break out. These are generally over mates, and may go on for several minutes. The combatants invariably emerge with their white shirt fronts covered in mud and blood.
The strong territorial urges of all colonial penguins makes moving through their rookeries a difficult if not dangerous experience. In order to reduce the attentions of their peers, the birds adopt a nonaggressive stance which penguin biologists have called the “slender walk.” With flippers pulled close to the body and head down, they waddle doggedly to their destination.
Rockhoppers have modified the slender walk into what seems like a mad hopping dash, punctuated by brief stops on top of larger rocks or clear ground, where they stretch their heads high and peer around—seemingly looking for the safest route. Once a path is chosen, they hop onwards, ignoring the pecks and flipper beatings of nest inhabitants they pass.
Strangely, if rockhoppers feel threatened, and are not guarding a nest, they will crowd together, seeking protection in numbers, but as soon as the threat is gone it is back to their usual ways, bickering amongst themselves.
By late October, the breeding birds have decided on their mates for the season, and spend much of their time displaying, grooming each other and working on their nests. Male birds with nests on the edges of the colony wander around collecting stones, vegetation, even old penguin bones as offerings for their mate. The contributions are accepted by the female after an exaggerated head swinging display, then positioned on the nest. For male birds near the centre of the colony, it is not generally worth the beatings to search far afield, so they gather whatever is close at hand and plentiful—often a neighbour’s nest.
Mating soon follows. It is normally initiated by the male fluttering a flipper against the female’s body. Once coerced, she lies on her front while he stands up on her back. The event has been likened to surfing, for the male anyway.
A week later, two eggs are laid.
The actual calendar date for laying—indeed, for the whole nesting cycle—varies considerably throughout the rockhopper penguin range. Closely linked to sea temperature, the timing depends on the whereabouts of the rookery. At the northern rookeries, where summer sea temperatures are 14-16°C, laying commences in September, while further south, where the water temperature may be as low as 2°, eggs are not laid until December. On Campbell Island, the summer sea temperatures are about 9° and the rockhoppers lay their light blue-green eggs in early to mid-November.
The second egg laid is much larger than the first (2050 per cent by volume) and holds the prime candidate for survival to adulthood. The smaller first or “A” egg can be regarded as a back-up: if anything untoward should happen to the large egg, this one will take over.
However, the A egg doesn’t usually get the chance. For a start, the larger B egg gets the warmer incubating position directly under the mother’s brood patch (a patch of bare skin). It is about four degrees warmer here. The A egg’s cooler, less favourable position also means it is more likely to be accidentally knocked out of the nest or snatched by a skua. Furthermore, if the small egg does manage to hatch, the chick from the larger egg literally starves its smaller brother or sister to death by monopolising the food brought by the parent bird. Only in years when the food supply is abundant will two chicks be successfully raised.
Eggs fall from nests with monotonous regularity, either through clumsiness or during fights. Once it is away from the nest, the parents seem to lose all interest in the egg, writing it off as just another rock. (Even if they wanted to, they have no means of returning the egg to the nest.) Such mislaid eggs don’t last long; the colony’s resident skuas are quick to move in.
Skuas are the keas of the Southern Ocean, fearless and inquisitive. They are opportunists, always on the lookout for unattended eggs. Once a skua has seen an egg it will swoop in and land among the penguins, who will start up a tremendous chorus of shrieks and cries, and try to attack the intruder. Occasionally they succeed, dragging the skua down and pecking the life out of it. In most cases, though, the skua snatches the egg and flies to the outskirts of the colony to eat it. The large number of broken eggs around the edges of rockhopper colonies bear witness to the effectiveness of the skuas and the clumsiness of the penguins.
Once incubation begins, quite suddenly the colonies become quiet. There are fewer birds, less fighting, less displaying. Why? Because the males have left for sea for nine days to fatten up for their turn at incubating the eggs. When they return, the females will have spent up to 45 days without feeding, losing so much of their body weight that they become bony and angular.
During this period, with only one bird at the nests, skuas are even more aggressive. Crossing the line from scavengers to predators, they will attack birds nesting on the outskirts of the colonies, diving in and bodily pushing the penguin off its nest and seizing an egg. Sometimes they work in pairs, one skua harassing the rockhopper from one side while its mate steals an egg from the other.
Skuas are the penguins’ main predator on land, although giant petrels may occasionally take chicks or injured adults. Hooker’s sealions and New Zealand fur seals take some penguins at sea, especially near landing sites, but these animals never attack penguins on land.
Joining the males on their return in early December are the juvenile rockhoppers. Tassel-less and grey-chinned, they are not yet of breeding age (three years), and tend to congregate on the edges of the colonies or between the colonies and the sea. So, too, do the unsuccessful breeders and the odd straggler of other penguin species.
The mated males take over incubation of the eggs from their partners, who head to sea to regain condition. Some females seem reluctant to leave their eggs and may stay for several days after being relieved. The chicks hatch in mid-December, after a 33-day incubation. The male rockhoppers get the job of guarding the hatchlings while the females act as food-gatherers.
At about three weeks of age, the chicks move from the nests into crèches, allowing both parents to go to sea to supply the needs of their ever-hungry offspring. The chick crèches are near the centre of the rookeries, on top of boulders, where possible, to keep the young birds out of the muddy mess below. They crowd closely together, having not yet developed the adults’ argumentative traits. A few nonbreeding mature birds stay in the colony, possibly acting as minders.
Parents arrive back at shore late in the afternoons with bellies full of fish for the chicks. Landing in groups of 10-70 birds, they porpoise through the pounding surf, bull kelp and foam. Catching the back of a wave in, they clamber madly up the rocks and over each other, using claws, flippers and beak, trying to reach high ground before the next breaker arrives and sucks them back out to sea.
At a crèche, more than one chick may rush up to an arriving adult, peeping and waving its flippers in the hope of getting a meal. However, each chick has its own distinctive call, and adults recognise and feed only their own, driving strangers away with a flurry of pecks.
The chicks grow rapidly, and soon start losing their down, starting with the flippers. Crèches tend to break up at this point, and the now large chicks spend more time at their own nest sites. Yearlings, sometimes appropriately called “fats,” begin moulting. Overweight compared to the lean breeding birds, these scruffy-looking penguins stand around lethargically, slowly shedding feathers to reveal a shiny new blue-grey and white coat.
At about 65 days old, the chicks head down to the landing site for their initiation into a new world of surf, storms and hungry sealions. They have now lost their down and have mostly adult plumage, though without a full crest.
On discovering there are no chicks to feed, the breeding adults will head out to sea, too, to fatten up for their turn at moulting. Once moulted, they will spend five months at sea.
It is these five months, in contrast with the other seven of the rockhoppers’ year, that scientists know next to nothing about. Even where they go is a mystery. Probably north, to avoid the cold southern winter waters—although, strangely, they are rarely found beached on New Zealand shores.
Just as uncertain is their long-term future. Catastrophic decline in numbers over the past 40 years [see box page 64] leads scientists to question whether the birds will keep returning to Campbell Island. But if the fighting spirit of these plucky little penguins has anything to do with the outcome, then the rugged shores of New Zealand’s subantarctic outpost will continue to be home to the rockhoppers.